A top dead center and a bottom dead center of a well-known ordinary engine are fixed, and a compression ratio is constant, resulting in low ignition pressure and low heat-engine efficiency of a gasoline engine with power adjusted by adjusting an intake volume when at a low load, but the variable compression ratio engine can solve this problem.
The well-known variable compression ratio engine has a movable cylinder head type, a movable crankshaft type, a way of hydraulically changing a piston length and a way of changing the piston length by combining a spring and hydraulic pressure. There is a formed product of the movable cylinder head form, and it proves that the variable compression ratio engine can greatly save the oil consumption. The variable compression ratio engine of the movable cylinder head type and the movable crankshaft type has large movable parts, also increases the complexity of a cam and a power output shaft for driving an air valve, and is not widely popularized at present.
According to the solution for changing the piston by means of hydraulic pressure and by combining the spring and the hydraulic pressure, since the piston is a part moving at a high speed, a hydraulic pipeline is difficult to arrange reliably.
An inventor of the present invention designs a self-pumping variable compression ratio piston (2012204098128) in early days; the piston Is designed as a double-acting hydraulic cylinder; an inner piston of the hydraulic cylinder is connected with a connecting rod; the inner piston and a cylinder body are respectively provided with a control valve sleeve and a control valve element; and the control valve element is classified into an axial moving type and a rotating type. Inner cylindrical surfaces of both control valve sleeves are provided with a liquid passage respectively communicated with an upper hydraulic cylinder and a lower hydraulic cylinder; the middle of each control valve sleeve is a sealing section; the rotating-type control valve element is provided with a spiral liquid passage on an outer cylindrical surface; the axial moving-type control valve element is provided with an annular liquid passage in the middle of an outer cylindrical surface; the control valve element is provided with a central through hole; the central through hole is communicated with the liquid passage on the outer cylindrical surface; the central through hole is respectively communicated with the upper hydraulic cylinder and the lower hydraulic cylinder through a check valve; the liquid passage on the outer cylindrical surface of the control valve element can be communicated with an upper liquid passage and a lower liquid passage on the inner cylindrical surface of the control valve sleeve by rotating the control valve element with the spiral liquid passage on the outer cylindrical surface or axially moving the control valve element with the annular liquid passage on the outer cylindrical surface; when the liquid passage on the outer cylindrical surface of the control valve element is communicated with the liquid passage on the inner cylindrical surface of the valve sleeve, and when the upper hydraulic cylinder is pressed (a typical state is at a power stroke or nearby the bottom dead center), hydraulic oil of the upper hydraulic cylinder enters the control valve element from the upper hydraulic cylinder and flows into the lower hydraulic cylinder through the check valve so as to push the inner piston to move upwards, so that the piston length is reduced, simultaneously the inner piston moves upwards; when the sealing section of the control valve sleeve is opposite to the liquid passage on the valve element, the liquid passage on the valve element is neither communicated with the upper hydraulic cylinder nor communicated with the lower hydraulic cylinder, and the position of the inner piston is fixed; likewise, when the liquid passage on the outer cylindrical surface of the control valve element is communicated with the lower liquid passage on the inner cylindrical surface of the control valve sleeve, and when the lower hydraulic cylinder is pressed (a typical state is at a last phase of an intake stroke and an exhaust stroke), the hydraulic oil of the lower hydraulic cylinder enters the control valve element from the lower hydraulic cylinder and flows into the upper hydraulic cylinder through the check valve to push the inner piston to move downwards, so that the up and down movement of the inner piston is realized by moving the valve element, the length of the piston is changed, no conveying passage of the hydraulic oil is needed, and difficulty in configuring other parts is not increased; however, a small end of the connecting rod of the conventional engine is disposed at the axis of the piston, so that a control rod of the valve element must be installed on a side surface, resulting in an asymmetric structure of the piston; therefore, the cylinder head of the double-hydraulic-cylinder piston is not suitable for being installed by adopting a screw thread with a relatively simple structure, and the structure is relatively complex; the self-pumping variable compression ratio piston (2012204098128) in the early days does not consider the heat expansion problem of working liquid either the self-pumping variable compression ratio piston adopts the check valve, while the check valve is influenced by the movement acceleration of the piston, so that the working parameters are difficult to design.
The well-known engine is generally of a single-crankshaft type, while research and experiment are also done on a double-crankshaft engine; the double-crankshaft engine is provided with two crankshafts; each piston is simultaneously connected with the two crankshafts through connecting rods; the two crankshafts are meshed together; the two crankshafts rotate oppositely, so that the side pressure of the piston can be eliminated; meanwhile, the diameter of main shafts of the two crankshafts and a main shaft of the connecting rods can be reduced, thereby reducing the frictional loss; however, it can be known from some data that the engine may have an asynchronous phenomenon of the two connecting rods nearby the top dead center and the bottom dead center, resulting in instability in operation; the above-mentioned problems can be solved by adding a connecting shaft; the inventor finds through research that when the two crankshafts are coupled by virtue of gears, and then the power is output by virtue of a single drive shaft, since the energy output (a power stroke) and energy intake of the engine occur alternately when in operation, the coupled gear may frequently stay at a forward-backward driving state, and the working state of the coupled gears is extremely severe, which may lead to extremely short service life of the gears.